preemphasis: Pre-emphasis speech filter

Description

A pre-emphasis frequency filter for speech

Usage

preemphasis(wave, f, channel = 1, alpha = 0.9,
plot = FALSE, output = "matrix", ...)

Value

A new wave is returned. The class of the returned object is set with the argument output.

Arguments

wave: an R object.
f: sampling frequency of wave (in Hz). Does not need to be specified if embedded in wave.
channel: channel of the R object, by default left channel (1).
alpha: time constant, see Details.
plot: a logical, if TRUE plots the spectrogram of the filtered wave and the frequency response of the comb filter.
output: character string, the class of the object to return, either 'matrix', 'Wave', 'Sample', 'audioSample' or 'ts'.
...: other arguments to be passed to spectro except scale and osc that are set by default to FALSE.

Author

Jerome Sueur

Details

The function applies a pre-emphasis filter usually applied in speech analysis. The filter is a kind of high-pass frequency filter that amplifies the high-frequency content of the sample. The filter is defined with: $$y(n) = x(n) - \alpha \times x(n - 1)$$ where alpha is a time constant usually set between 0.9 and 1.

The frequency response of the filter is obtained with: $$H(f)=1+a^{2}-2 \times \alpha \times \cos(2 \times \pi \times f/f_{s})$$

Examples

Run this code

data(sheep)
fc <- 150
f <- sheep@samp.rate
alpha <- exp(-2*pi*fc/f)
res <- preemphasis(sheep, alpha=alpha, output="Wave")

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